A first-principles investigation of the phase stability of Ti2AlC with Al vacancies

Ti2AlC was predicted to bear Al-vacancy down to a sub-stoichiometry of Ti2Al0.5C. The phase instability beyond a critical Al content was attributed to occupation of the Ti–Al anti-bonding orbital, which reduces the coupling strength between Ti2C slab and Al atomic plane. The migration energy barrier of Al self-diffusion along the (0 0 0 1) plane was low, 0.83 eV, resulting in rapid out-diffusion of Al during oxidation and decomposition of Ti2AlC at high temperatures.